1. Field of the Invention
The present invention relates to a video projection display system of projecting and displaying a light image which has been obtained by modulating projected light, and an illumination apparatus for use in the video projection display system.
2. Description of the Related Art
There has been known a video projection display system of projecting and displaying, onto a screen or a like apparatus, a light image which has been obtained by modulating light rays from a light source based on an image signal pixel by pixel (e.g., in Japanese Unexamined Patent Publication No. 10-123512). The video projection display system disclosed in the publication employs a liquid crystal display (LCD) device, which is a light transmissive device, as a device (called as “light valve”) which modulates incident light from a light source. Further, the video projection display system uses an LED array comprised of a multitude of light emitting diode (LED) devices in an array, as a light source, to increase the light amount of projected light, and a group of condenser lenses which are disposed in front of the respective LED devices to substantially converge light rays outgoing from the respective LED devices into parallel rays.
It is desirable to use a light reflective device as shown by a digital micro mirror device (DMD), as a light valve, to increase the light amount of projected light. A system incorporated with the light reflective device has a merit that it is free from polarization dependency, namely, there is no need of using a polarized ray as an incident ray, unlike a system using a LCD device. The system using the light reflective device has been designed in an attempt to obtain a projected light image having a large light amount with use of a light source having the same light amount.
However, in case of using a DMD as a light valve, it is necessary to allow light to be incident onto a light receiving plane of the DMD with a direction of about 45° with respect to one side of the light receiving plane. Accordingly, in the case where an LED array is used as a light source, there is assumed an arrangement pattern as shown in FIG. 6A, for instance, wherein respective lens elements constituting a fly-eye lens are arrayed as opposed to the LED array to converge a bundle of rays generated in the LED devices. Specifically, a lens element 33 constituting the fly-eye lens opposing to a corresponding LED device 31 has a rectangular shape corresponding to the shape of the light receiving plane of the DMD, and is arranged in such a manner that one side of the lens element 33 is tilted relative to one side of a square effective area 30 by 45°, wherein the effective area 30 is defined by an optical system as an area capable of arranging all the lens elements 33 of the fly-eye lens.
In the arrangement pattern as shown in FIG. 6A, there is left a useless area in the effective area 30 where the lens unit 33 cannot be arranged. Furthermore, since the lens elements 33 are arrayed close to each other substantially without clearance, the LED devices 31 corresponding to these lens elements 33 are resultantly arranged close to each other, which may lower heat releasing ability of dissipated heat. If the heat releasing ability of dissipated heat of the LED array is lowered, it is highly likely that temperature rise in the LED array is intolerable. Such a phenomenon may obstruct miniaturization of the illumination apparatus and the video projection display system.